Willis, San Francisco's six-time Pro Bowl linebacker, is scheduled to undergo an MRI exam on the injury. Jim Harbaugh revealed the news in his Monday press conference.

Willis landed awkwardly while trying to tackle Wayne on a third-down pass completion that went for a 25-yard gain. It took place in the third quarter of Sunday’s 27-7 loss to the Colts.

It’s not known if Willis will be able to play this Thursday against the St. Louis Rams.

“We’ll leave that to the evaluation and the treatment of the doctors and trainers,” Harbaugh said.

Willis has made 25 consecutive starts in the regular season and postseason combined. The All-Pro inside linebacker has only missed four starts in six seasons. Willis' status will be watched closely this week even more so with Aldon Smith being placed on Reserve/NFI.

As for other key members of the 49ers with health situations being monitored by the team, Harbaugh said tight end Vernon Davis continues to be evaluated with a hamstring injury, the one he suffered in a Week 2 loss at Seattle.

Veteran cornerback Nnamdi Asomugha, like Willis, will also receive an MRI exam. Only Asmougha's will take place on the knee he injured in the end of Sunday’s game while trying to tackle Colts running back Ahmad Bradshaw from behind.

Harbaugh was also asked about the status of second-year running back LaMichael James who has been inactive the first three weeks of the regular season.

“He’s getting back,” Harbaugh said of the second-round draft pick from 2012.

The 49ers coach also didn’t proclaim that James would be among the team’s 46 active players for future gamedays.